The present invention is based on a fibre mat for the cleaning of contaminated air. Contaminated air passes through the fibre mat from its front to its back. During this passage, solid particles and drops of liquid (designated as aerosols) are absorbed. These absorbed particles can concentrate at certain points in the filter mat. Consequently, the fibre mat's cleaning efficiency is lowered because these parts of the fibrous mass then prevent passage of contaminated air. The resultant increased pressure drop across the filter is a great disadvantage.
Depending on the type of contamination, different types of filter are required for filtering oil-laden air not only from lathes, milling machines, drills, grinders and hardened drilling tools, but also from machines used in cold rolling, hot rolling, hot forming, die casting, wire drawing and the manufacture and machining of rubber, plastic and so on. In the foregoing application areas, the air flow through the filter is large, normally between 500 and 200,000 m3 per hour. The filter should be able to withstand continuous use. This means that, for at least one year, and without stoppages for draining and cleaning, it must be able to filter air that contains aerosols, usually between 0.5 and 100 mg per cubic meter of air. The filter must be self-draining. This means that the oil trapped by the filter has to be drained while the filter is still in use and with the served machinery still running. Throughout its entire service life, the filter should, when filtering emulsion aerosols and oil aerosols, have a collection efficiency of between 80 and 98 percent. The collection efficiency can be measured using instruments such as the “Dust Track TSI”. Furthermore, the filter should be washable and capable of being reused at least five times.
Provided that it can trap the contaminants in the air passing through it, the filter can be of any type whatsoever.
Fibres are a suitable material for filters. Glass fibres of less than 20 micrometers are to be preferred. Glass fibres with a fibre size in the range of 3-12 micrometers are particularly suitable. Fibrous material can be held together by needling. In this process, needles are stuck into the material, thereby pulling some of the surrounding fibres with them. These fibres take up a transversal alignment and hold the material together, even after the needles have been pulled out. As the fibres have been needled securely to each other, rather than joined using a bonding agent, the risk of auto-ignition in the oil filter is considerably reduced.